Thermostat



THERMOSTAT Filed Jan. 15, 1937 INVENTOR Patented July 30, 1940 UNITED STATES PATENT OFFICE THERMOSTAT Application January 15, 1937, Serial No. 120,730

8 Claims.

In electrically operated systems and particularly low voltage systems provided by transformers, the voltage and therefore the amperage usually varies to some extent for different loads.

5 In control systems having thermostats operating on low voltage provided by transformers, it is usually required that the transformers be of a character which will not overheat in the event of a short circuit. It has been found that where .10 transformers made to meet the above requirement are employed, there is an appreciable difference in the' voltage and therefore in the amperage for different loads. That is, under heavy loads which require high amperage from the 15 transformer the voltage will be relatively low, while for light loads that require comparatively low amperage from the transformer the voltage will be relatively high. As a result, in a control system having a thermostat provided with an electric heater in circuit with the transformer for heating and influencing the operation of the thermostat, the effect of the heater will be difierent for different voltage or amperage. Or in other words, the same heater will not be as effec- 5 tive with one load as it will be for another, which is of course objectionable.

Accordingly it is the principal object of my invention to provide a thermostat heated by electrically energized heating means in circuit with 30 a load and a transformer, and one in which the thermostatic element will receive a substantially constant heat input from the heating means irrespective of the magnitude of the load.

The invention consists in the improved con- 35 struction and combination of parts, to be more fully described hereinafter and the novelty of which will be particularly pointed out and distinctly claimed.

In the accompanying drawing, to be taken as a part of this specification, I have fully and clearly illustrated my invention, in which draw- Figure 1 is a diagrammatic view of a temperature control system embodying my invention, and 45 Fig. 2 is a view of a modified form of my invention. 1

Referring to the drawing by characters of reference the numeral i designates in general my thermostat and the numeral 2 designates a con- 50 trol which may be a motor for controlling a'heating apparatus. The thermostat i is preferably operated on low voltage provided by a trans: former 3 having the usual primary coil 4 and secondary coil 5. Main lead wires 6, i may con- 55 nect the transformer primary i to the usual 110 v. line and lead wires 8, 9 may connect the transformer primary to the control 2. The thermostat 'I may control the circuit of the control 2 through controlling a relay l0 which, in the present instance, is the load, it being understood 5 however that the load may be any electrically operated device. The load or relay l0 may beof the conventional type having an electromagnet H and a switch l2, the switch being located in the lead wire 9 that leads from the transformer 10 primary 4 to the control 2.

My thermostat I preferably includes a supporting member or base 14 on which is mounted a temperature responsive element or bimetal blade I5. The blade l5 may extend in a general ver- 15 tical direction and have its lower end secured to and'adjacent the lower end of the base I4.

A contact member i6 is mounted on and secured. to the base l4 for cooperation with the blade l5 to control the circuit of the load or relay Ii]. The contact I6 is preferably in the form of a screw and may be adjustably screw threaded into a metallic supporting member I! that may be rigidly secured to the base 14. Preferably the contact I6 is located at one side of the blade i5 and adjacent the upper or free end thereof. The contact H5 is connected to the electromagnet H by a lead wire I8 and the electromagnet may be connected to the transformer secondary 5 by a lead wire 19. Preferably a magnet 20, which may be of the so-called permanent U-shaped type, is provided for attracting and holding the blade l5 in engagement with the contact l6. As is well known, the magnet 20 serves to determine the differential operation of the thermostat l and also serves to prevent sparking between the blade l5 and the contact Hi.

In order to provide a thermostat having electrically energized heating means in circuit with a load and with the circuit including a trans- 40 former which may be of the type embodying such construction that it has poor voltage regulation that said thermostat will be subjected to a substantially constant heat from the heating means irrespective of the magnitude of the load, 4 I provide two heaters 2| and 22 and place the heater 2! in parallel circuit with the load or relay l0 and place the heater 22 in series circuit with the load. The heaters 2i and 22, which are electrical resistances, may be termed the 50 voltage and amperage heaters respectively, and may be mounted on the base Hi on opposite sides of the blade l5, as shown. The voltage heater it, which may be a wire, has one end connected to the contact supporting member II and has its other end connected by a lead wire 24 to the same side of the transformer secondary 5 as the load or relay Ill. The other side or pole of the transformer secondary 5 is connected by a lead wire 25 to one end of the amperage heater 22, and the other end of the amperage heater is connected to the blade l5, preferably by a jumper wire 26. Thus the heater 2| is in parallel circuit with the load or relay l0 and the heater 221s in series circuit with the load or relay I0.

When the blade I 5 becomes dissatisfied and calls for heat, the blade will engage the contact l6 which will close the series circuit of the relay Ill and amperage heater 22 and also will close the parallel circuit 'of the voltage heater 2|.

The series circuit of the relay I0 and amperage heater 22 is as follows: From the contact l6 through lead wire l8, relay electromagnet I, lead.

wire I 9, transformer secondary 5, lead wire 25, amperage heater 22, blade l5 and back to the contact I 6. The parallel circuit of the voltage heater 2| is as follows: From the contact I6 through the voltage heater 2|, lead wire 24,

- 22 preferably are selected such that they will.

transformer secondary 5, lead wire 25, heater 22, lead wire 26, blade I5 and back to the contact l5. Upon being energized the relay M will close the circuit of the control 2 which will operate to cause additional heat to be supplied to the room or other enclosed space to be heated.

The heaters 2| and 22 are selected so that together they will generate heat and raise the temperature of blade l5 to a desired temperature above the temperature of a room or other enclosed space to be heated. For the purpose of exposition it will be assumed that the combined heat generated by the two heaters will raise the temperature of the blade 2 F. above average room air temperature, and that the blade I5 is set to close the circuit of the load or relay l0 when the blade is at a temperature of 69 F. and to open the circuit of the relay II) when the blade is at a temperature of 73 F. The heaters 2| and have a quick heating-up time and a quick coolingdown time When the average room temperature has been increased by the heating apparatus to 71 F. the blade l5 will be 73 F. because of the 2 F. increase in the blade temperature above room, air temperature caused by the heaters 2| and 22, and the blade will move out of engagement with contact l6 and open the circuits of the relay Ill and the heaters 2| and 22. The relay l0, upon being deenergized, will open the circuit of the control 2 which will act to stop or decrease the heat input into the room. The heaters 2| and 22 will co'ol very quickly and after a short time the blade I5 will be heated only by the room air. When the temperature of the room, and therefore the temperature of the blade l5, decreases to 69 F., or whatever temperature 'it is set to call for heat, the blade will again engage contact I6 to close thecircuit of and energize the relay l0 and heaters 2| and 22. The purpose of the heaters 2| and 22 is to prevent unduly long operating periods of a heating apparatus or, in other words, the heaters compensate for the time period or time lag between the time of heat input to the room and the time when such heat input raises the temperature of the blade I5 to the temperature for which it is set to cut-out the heating apparatus or stop heat input to the room.

When my thermostat is employed with a load that requires only relatively low amperage, the voltage will be high and under these conditions a down and heater 2| will be less effective, but

because of the higher amperage passing through the amperage heater 22 the total heating efiect of both heaters will remain substantially constant. Thus it will be seen that my thermostat may be employed with loads of varying magnitude, or with loads of different magnitude, without variation in the effectiveness of the blades electric heating means. It will also be seen that my thermostat eliminates the need of providing heaters of different resistances for different loads when using one standard type of transformer.

Referring now to Fig. 2 the modified form of my thermostat shown in this view is similar to that shown in Fig. l, but differs therefrom in that the blade |5 itself is utilized as one of the resistance heaters. In Fig. 2 the blade I5 is employed as the amperage heater, but it is to be understood that the blade may serve either as the amperage heater or as thevoltage heater, as desired.

What I claim and desire to secure by Letters Patent of the United States-is: v

1. In a control system, an electrical energy supply, an electrical load, a temperature respontion thereof, said heating means being in parallel circuit with said load, and a second electric heating means in heat transfer'relation with said.

responsive means for influencing the operation thereof, said second-named heating means being in series circuit with said load and also with said first-named heating means.

2. In a control system having a transformer and a load in circuit therewith, a contact member, a temperature responsive element cooperable with said contact member to control the circuit of the load, said element also acting as a resistance heater for heating and influencing its own operation, and an electric heater in heat exchange relation with said element for heating and influencing the operation of said element, said secondnamed heater being electrically connected to the transformer and in parallel circuit with the load and in .series circuit with said element.

3. In a control system having a transformer and a load in circuit therewith, a contact member, a temperature responsive element cooperable with said contact member to control the circuit of the load, said element, also acting as a re member.

4. In a control system having a transformer and a load in circuit therewith, a contact member, a temperature responsive element cooperable with said contact member to control the circuit of 35 the load, an electric heater connected to the transformer and in parallel circuit with the load, said heater being arranged in heat exchange relation with said element to heat and influence operation of said element, and a second electric heater for heating and influencing the operation of said element, said second-named heater being connected to the transformer and in series circuit with the load and with said first-named heater, both of said heaters being controlled by said element and energized when said element becomes dissatisfied.

5. In a control system, electrically operated means having a source of electrical energy, a temperature responsive element having a contact member, a contact member in circuit with said means and said source and cooperable with said first-named contact member, an electric resistance member positioned in thermal transfer relation to said element, a second electric resistance member positioned in thermal transfer relation to said element, said resistance members jointly being operable to supply heat to said element at a substantially constant rate irrespective of the current required by said operated means, said resistance members being in circuit with said source and said contact members, one of said resistance members being operable to supply heat to said element in direct proportion to the square of the sum of the current flow through said means and through the other of said resistance members, and the other of said resistance members being operable to supply heat to said element in direct proportion to the square of the voltage impressed on said electrically operated means.

6. In an electrical system for use with electrical loads requiring various rates of current flow including a source of electrical energy which may be subject to substantial voltage changes due to changes of current supplied, a temperature responsive means including a switch means and a combined temperature sensitive and electric resistance member for actuating said switch means, a heating means positioned in thermal transfer relationship to said member, said heating means being directly responsive to the square of the voltage impressed on said electrically operated means, said combined member being directly responsive to the square of the total current flowing in said system, the heating effect of said combined members and said heating means being so proportioned relative to each other and to said energy source that the joint heating effect of said combined members and said heating means is substantially constant regardless of the current supplied to the electrical load.

'7. In an electrical system, an electrically operated apparatus, means in series circuit therewith and operable to control the operation thereof, means operable during a condition of said apparatus for maintaining a combined heating effect on said control means, said heating effect being proportional to the square of the current controlled by said means and to the square of the voltage impressed on said apparatus irrespective of changes in the current required by said apparatus, said last-named means producing a substantially constant heating efiect on said firstnamed means irrespective of any change in current which might be required by said apparatus.

8. In a control system, an electrically operated apparatus, means in series circuit with said apparatus and operable to make and break an electrical circuit to said apparatus, said means being responsive to a heating effect variable with the square of the magnitude of the current controlled thereby, a second heating means in parallel circuit relation with said apparatus and effective to supply heat according to the square of the voltage across said apparatus irrespective of changes in current required thereby, said second-named means being so proportioned relative to said firstnamed means that the combined heating effect of said first-named and said second-named means is substantially constant regardless of the magnitude of the current required by said apparatus.

EARNEST J. DILLMAN. 

